Open cracks and joints in concrete or asphaltic concrete pavements present a path for intrusion of water into the base and sub-base of the highway. Water intrusion beneath the pavement causes erosion of the foundation and accummulated water can cause the pavement to break up due to alternate freezing and thawing cycles. Water intrusion ultimately contributes to the failure of the pavement structure.
Various types of crack and joint fillers or sealers have been developed to solve the problems of open cracks and joints. The great majority of such crack and joint fillers are asphaltic in nature, and the incorporation of rubber or other elastomers into an asphalt-based filler increases the flow resistance, the low-temperature flexibility and the adherence of the fillers to the crack or joint walls to provide a longer lasting seal which can better resist pavement contraction and expansion during freeze-thaw cycles. The prior asphalt or rubber-asphalt sealers must be "hot-poured" at temperatures ranging from about 300.degree. to about 400.degree. F., and they are typically applied from double boiler, oil-jacketed melter applicators which are equipped with an agitator and separate temperature indicators for the oil bath and the melting vat.
Many problems have developed in the utilization of such hot-poured fillers, including the danger of fire and other accidents encountered in the use of combustion heaters, the thermal degradation of the fillers as they are maintained at temperatures on the order of 300.degree. to 400.degree. F. over long periods of time, the necessary cleaning of the heating and applying apparatus at the end of each working day, and the necessity for specialized vehicles to transport the heavy and cumbersome heating equipment. All in all, the utilization of hot-pour crack and joint fillers is both dangerous and expensive.
Several attempts have been made in the past to provide water-based emulsions of asphalt-rubber crack and joint fillers which can be poured at ambient temperatures and which avoid all of the dangers and expenses of the conventional hot-poured fillers. However, prior to the present invention, it has not been possible to provide an aqueous-based, cold-pour joint and crack filler capable of meeting ASTM Specification D1190 which has been adopted by a majority of the State Highway Administrations as the standard for asphalt-rubber joint and crack fillers. The exacting standards of the ASTM Specification D1190 define the functional characteristics required of asphalt-elastomer blends and thus would apply to that portion of the emulsified filler remaining after the emulsion water has been evaporated. Generally, these requirements of ASTM D1190 include a residue penetration at 77.degree. F. of 90 or less, flow at 140.degree. F. of 5 mm or less, and passing five complete bonding cycles at 0.degree. F. The test methods for all three of these specifications is set forth in ASTM Test Method D1191.
The present invention provides an aqueous emulsion, the residue of which meets the requirements of the ASTM 1190 Specification. Generally, the emulsion of the present invention includes a chemically-modified asphalt which is the reaction product of certain ingredients reacted at an elevated temperature for an extended period of time under reflux, and the reaction product is then emulsified in an emulsification medium including water, a surfactant, and a thixotropic agent.
Generally similar reaction products from different reaction mixtures have been defined and disclosed in several previous patents assigned to the assignee of the present invention, namely U.S. Pat. Nos. 4,394,481; 4,507,365; 4,456,633; and 4,419,489. In particular, U.S. Pat. No. 4,419,489 proposes an aqueous emulsion for possible use as a joint sealer for highways or the like, but the disclosed emulsion cannot meet the ASTM Specification D1190. Similar emulsions are also disclosed in U.S. patent application Ser. No. 839,482, filed Mar. 14, 1986 and assigned to the assignee of this invention, but again the disclosed emulsions would not meet the requisite ASTM Specification.
The specific emulsion of the present invention includes the reaction product of asphalt, an extender oil, a mixture of elastomers, preferably including liquid rubber and at least one block copolymer of an ethylenic monomer and a conjugated diene, an acrylamide and styrene. These reaction products are reacted at an elevated temperature, typically on the order of 300.degree. F. to 400.degree. F. (149.degree. to 204.degree. C.) for an extended period of time, on the order of 20 to 30 hours, under reflux. The reaction product is emulsified in an aqueous emulsification medium, preferably a medium containing from about 0.5 to about 7% by weight surfactant, and from about 0.01 to about 0.20% of a high molecular weight acrylamide as a viscosity control ingredient.
The final emulsion is formed in suitable apparatus, such as a colloid mill or the like, and it contains from about 30% to about 45% emulsification medium and from about 55% to about 70% of the asphaltic ingredient.
The resulting asphalt emulsion possesses suitable viscosity and flow characteristics to be applied as a crack and joint filler or sealant either by simply pouring the emulsion into the crack or by filling the crack with the emulsion under pressure dispensed from a wand.